Air-conditioning apparatuses, such as a multi-air-conditioning apparatus for a building, include an air-conditioning apparatus configured such that a refrigerant is circulated from an outdoor unit to a relay device (relay unit) and a heat medium, such as water, is circulated from the relay unit to each indoor unit to reduce conveyance power for the heat medium while circulating the heat medium, such as water, through the indoor unit and achieve a cooling and heating mixed operation (see, for example, Patent Literature 1).
A circuit for injecting a liquid refrigerant into a compressor from a high-pressure liquid pipe in a refrigeration cycle in order to reduce a compressor discharge temperature and an air-conditioning apparatus capable of controlling a discharge temperature at a preset temperature, irrespective of an operation state, have been recently developed (see, for example, Patent Literature 2).
Another air-conditioning apparatus which uses, as a refrigerant, R32 that is a refrigerant having a relatively low global warming potential (GWP) and performs injection (refrigerant supply) from an outlet side of a gas-liquid separator in a high-pressure liquid pipe of a refrigeration cycle into a compressor (high-pressure shell compressor) in which the inside of a sealed container is at a discharge pressure atmosphere has been recently developed (see, for example, Patent Literature 3).